rosin(noun, verb) noun1. any of a class of solid or semisolid viscous substances obtained either as exudations from certain plants or prepared by polymerization of simple moleculesSimilar word(s): resinDefinition categories: substance verb1. rub rosin onto- rosin the violin bowDefinition categories: contact, rubSentences with rosin as a verb:- We waited expectantly as the guest violinist rosined his bow in preparation to playing.